Surface grinding method for workpiece and surface grinder

ABSTRACT

[Problem] To enable efficiently grinding a workpiece of a hard brittle material, a difficult-to-cut material, or others at a moderate high load. 
     [Solution Means] When surface-grinding a workpiece by a grinding wheel, a grinding load is monitored while the grinding wheel is reduced in cut-in speed when the grinding load rises and the cut-in speed is increased when the grinding load falls. Respective cut-in speeds with which the grinding wheel has a slower cut-in speed at a larger grinding load have been set in a manner corresponding to a plurality of respective load thresholds of the grinding load, and after starting grinding at a predetermined speed, the grinding wheel is decelerated or accelerated to a corresponding cut-in speed every time the grinding load rises or falls to a predetermined load threshold.

TECHNICAL FIELD

The present invention relates to a surface grinding method for aworkpiece and a surface grinder for surface-grinding a workpiece.

BACKGROUND ART

When grinding a workpiece of a hard brittle material such as a siliconwafer to be used for manufacturing a semiconductor device, in a surfacegrinder equipped with a cup-shaped grinding wheel, a load current of agrinding wheel spindle drive motor is monitored, while the grindingwheel at the distal end of a grinding wheel spindle is caused to cut inat a predetermined cut-in speed to perform in-feed grinding of theworkpiece on a rotating table, and when the load current of the grindingwheel spindle drive motor exceeds a predetermined threshold due toloading of the grinding wheel, the grinding wheel is withdrawn tointerrupt grinding, and the grinding wheel is then again caused to cutin into contact with the workpiece to thereby promote self-sharpening ofthe grinding wheel (Patent Document 1).

PRIOR ART DOCUMENT Patent Document

[Patent Document 1] Japanese Published Unexamined Patent Application No.2006-35406

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

With such a conventional grinding method, the grinding wheel is causedto cut in at a predetermined cut-in speed, on the other hand, thegrinding wheel is once withdrawn to interrupt grinding when loadingoccurs in the grinding wheel during grinding, and the grinding wheel isthereafter again caused to cut in to promote self-sharpening of thegrinding wheel. Therefore, not only can the workpiece not be ground in ahigh-load state with high grinding efficiency of the grinding wheel, butas a result of the grinding cycle being prolonged, it has also beendifficult to efficiently grind the workpiece in a short time.

Conventional grinding methods other than the grinding method of PatentDocument 1 also include a grinding method of causing the grinding wheelto cut in at a constant cut-in speed with respect to the workpiece, anda grinding method (hereinafter, referred to as a common grinding method)of varying the feed speed sequentially in a speed reducing directionaccording to a cutting-in feed amount of the grinding wheel for a roughgrinding feed, a semi-finish grinding feed, and a finish grinding feedwhile performing grinding.

However, with the former grinding method, the abrasion loss of thegrinding wheel, the removal amount of the workpiece, and the cut-inamount of the grinding wheel may lose balance during grinding to lead toa sudden rise in grinding load or abrasion of only the grinding wheel insome cases, and it has been difficult to efficiently and stably grindthe workpiece in a high-load state with excellent grinding efficiency ofthe grinding wheel.

Also with the latter grinding method, it has been impossible for thefollowing reason to efficiently and stably grind the workpiece in ahigh-load state with excellent grinding efficiency of the grindingwheel. Particularly when grinding a workpiece of a hard brittle materialwhich is high in hardness and brittle, because the feed speed of thegrinding wheel is varied so as not to cause an overload state due tocut-in of the grinding wheel while performing the grinding, it isnecessary to slow the cut-in speed of the grinding wheel to perform thegrinding over a long time.

However, in the case of such a hard brittle material, self-sharpening(grains change) of the grinding wheel surface occurs several timesduring grinding, and the grinding load greatly changes up and down. Thisis because the grinding wheel is dull before self-sharpening, whereasonce self-sharpening of the grinding wheel occurs, the grinding wheelhas increased cutting edges to be suddenly improved in sharpness. As aresult, the coefficient of friction between the grinding wheel andworkpiece changes, and the grinding load greatly changes up and down, sothat stably grinding efficiently in a short time at a high load withexcellent grinding efficiency is impossible.

Also, it is often the case during self-sharpening that an axial distancebetween the grinding wheel spindle and rotating table is reduced becauseof sudden thermal displacement of the grinding wheel, workpiece, and/ormachine due to an increase in frictional heat. This is equal to anincreasing cut-in speed of the grinding wheel, which serves as a factorfor an intensive rise in grinding load. Then, if the grinding loadexcessively rises, there is a possibility such that the machine mayterminate machining based on detection of an abnormal grinding load, andthe grinding wheel and/or workpiece may be damaged or the machine may bedamaged in the worst case.

In view of such conventional problems, the present invention aims atproviding a surface grinding method for a workpiece and a surfacegrinder capable of efficiently grinding a workpiece of a hard brittlematerial or others at a moderate high load and capable of preventingdamage to the workpiece and/or grinding wheel and further to the machinedue to a sudden rise etc., in grinding load, and moreover capable ofreducing grinding wheel abrasion loss.

Means for Solving the Problem

A surface grinding method for a workpiece according to an aspect of thepresent invention is, when surface-grinding a workpiece by a grindingwheel, monitoring a grinding load while reducing the grinding wheel incut-in speed with a rise in the grinding load.

Also, a surface grinding method for a workpiece according to anotheraspect of the present invention is, when surface-grinding a workpiece bya grinding wheel, monitoring a grinding load while reducing the grindingwheel in cut-in speed when the grinding load rises and increasing thecut-in speed when the grinding load falls.

In addition, respective cut-in speeds with which the grinding wheel hasa slower cut-in speed at a larger grinding load may have been set in amanner corresponding to a plurality of respective load thresholds of thegrinding load, and after starting grinding at a predetermined speed, thegrinding wheel may be decelerated or accelerated to a correspondingcut-in speed every time the grinding load rises or falls to apredetermined load threshold.

Also, a returning load threshold higher than a maximum load threshold atcut-in time of the grinding wheel may have been set, and the grindingwheel may be returned at a predetermined return speed while grindingwhen the grinding load exceeds the returning load threshold. A cut-inand return of the grinding wheel may be repeated before spark-out.

When the grinding load exceeds a load threshold for implementation of aspeed limit, even if the grinding load thereafter falls to a loadthreshold of a predetermined cut-in speed, the grinding wheel may becaused to cut in at a limit cut-in speed slower than the predeterminedcut-in speed, that is, the cut-in speed may not be made faster than thelimit cut-in speed.

A surface grinder according to an aspect of the present invention is asurface grinder which in-feed grinds a workpiece by a grinding wheel,and includes a grinding load measuring means that measures a grindingload of the grinding wheel during grinding, a speed setting means inwhich a plurality of grinding wheel cut-in speeds are set correspondingto a plurality of load thresholds, and a speed control means thatcompares the grinding load during grinding with a load threshold whileaccelerating or decelerating the grinding wheel, on the basis of eachload threshold, at a cut-in speed corresponding to each load thresholdso that the grinding wheel is reduced or increased in cut-in speed witha rise or fall in the grinding load.

Effects of the Invention

According to the present invention, there are advantages of beingcapable of efficiently grinding a workpiece of a hard brittle materialor others at a moderate high load and capable of preventing damage tothe workpiece and/or grinding wheel and further to the machine due to asudden rise etc., in grinding load, and moreover being capable ofreducing grinding wheel abrasion loss.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a surface grinder showing a first embodimentof the present invention.

FIG. 2 is a perspective view of a main portion of the same.

FIG. 3 is a block diagram of a control system of the same.

FIG. 4 is a speed table of the same.

FIG. 5 is a flowchart of a grinding operation of the same.

FIG. 6 is a view showing changes in grinding load etc., of the same.

FIG. 7 is a block diagram of a control system showing a secondembodiment of the present invention.

FIG. 8 is a flowchart of a grinding operation of the same.

FIG. 9 is a speed table of the same.

FIG. 10 is a view showing changes in grinding load of the same.

FIG. 11 is a block diagram of a control system showing a thirdembodiment of the present invention.

FIG. 12 is a first speed table of the same.

FIG. 13 is a second speed table of the same.

FIG. 14 is a speed table showing a fourth embodiment of the presentinvention.

FIG. 15 is a block diagram showing a fifth embodiment of the presentinvention.

FIG. 16 includes waveform diagrams of speed changes of the same.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described indetail based on the drawings.

FIG. 1 to FIG. 6 illustrate the first embodiment of the presentinvention. When in-feed grinding a workpiece W of a hard brittlematerial such as a sapphire wafer by a cup-shaped grinding wheel 1, asurface grinder 2 as shown in FIG. 1 and FIG. 2 is used. The surfacegrinder 2, as shown in FIG. 1 and FIG. 2, includes a rotating table 3 onan upper surface of which a workpiece W is detachably mounted, aworkpiece drive means 4 such as a motor that drives the rotating table 3so as to rotate about a vertical axis center in an arrow a direction, agrinding wheel spindle 5 vertically movably arranged over the rotatingtable 3, a grinding wheel drive means 6 such as a motor that drives thegrinding wheel spindle 5 so as to rotate about a vertical axis center inan arrow b direction, the grinding wheel 1 that is detachably mounted atthe lower end of the grinding wheel spindle 5 and surface-grinds theworkpiece W on the rotating table 3 by a rotation in the arrow bdirection, and a grinding wheel feed means 7 that feeds the grindingwheel 1 via the grinding wheel spindle 5 in a cutting-in direction c anda returning direction d that are vertical directions. In addition, therotating direction of the rotating table 3 and the grinding wheel 1 isarbitrary.

FIG. 3 shows a control system that controls grinding operation of thesurface grinder 2. The control system has, for example, a sizing controlmeans 10 and a grinding wheel cut-in/return control means 11, besides anNC means 9 that controls a common grinding operation related to in-feedgrinding of the surface grinder 2.

The sizing control means 10 measures the dimensions of a workpiece Wduring grinding by a size measuring means 12, and performs control so asto issue a spark-out instruction to the grinding wheel feed means 7 whenit has reached a predetermined spark-out period in order to finish theworkpiece W with a predetermined dimensional accuracy by spark-out.

In addition, the grinding wheel feed means 7, if a spark-out instructionis received, stops feeding the grinding wheel spindle 5 so that thegrinding wheel 1 continues machining of the workpiece W at thatposition. When there is no sizing control means 10, a spark-outinstruction may be issued when a predetermined cut-in amount is reachedfrom the start of grinding of the workpiece W or when a predeterminedtime has elapsed.

The grinding wheel cut-in/return control means 11 is for monitoring agrinding load during grinding of the workpiece W while controlling thecut-in and return of the grinding wheel 1 so as to efficiently grind theworkpiece W at a moderate high load of high grinding efficiency, and hasa function of reducing the cut-in speed of the grinding wheel 1 with arise in grinding load, a function of repeating a cut-in and return ofthe grinding wheel 1 when the grinding load has risen to near an upperlimit, and a function of accelerating the grinding wheel 1 with a fallin grinding load.

The grinding wheel cut-in/return control means 11 specifically has agrinding load measuring means 13 that measures a grinding load of thegrinding wheel 1 during grinding, a speed setting means 14 that sets acut-in speed or return speed of the grinding wheel 1 for each loadthreshold, and a speed control means 15 that controls the grinding wheelfeed means 7, through a comparison of an actual grinding load duringgrinding with a load threshold, at a cut-in speed or return speed set bythe speed setting means 14 according to an increase or decrease in thegrinding load.

The grinding load measuring means 13 is structured so as to measure agrinding load of the grinding wheel 1 during grinding according to achange in a current or power flowing in the grinding wheel drive means 6or torque, etc. The speed setting means 14 has such a speed table asshown in FIG. 4. In the speed table, load thresholds L1 to L7 (N·m) atwhich grinding load increases in stages and cut-in speeds V0 to V7(mm/min) that increase or decrease in stages corresponding to therespective load thresholds L1 to L7 (N·m) are set for each operation ofa high-speed cut-in, a fast cut-in, an intermediate cut-in, a slowcut-in, a slow return, an intermediate return, a fast return, and anemergency return.

The high-speed cut-in is a cut-in when the grinding wheel 1 contacts theworkpiece W and starts grinding, and its high-speed cut-in speed V0 isset to 0.5 (mm/min). The fast cut-in is set to a fast cut-in speedV1=0.3 (mm/min) for the load threshold L1, the intermediate cut-in isset to an intermediate cut-in speed V2=0.1 (mm/min) for the loadthreshold L2, and the slow cut-in is set to a slow cut-in speed V3=0.05(mm/min) for the load threshold L3.

On the other hand, the slow return is set to a slow return speedV4=−0.05 (mm/min) for the load threshold L4, the intermediate return isset to an intermediate return speed V5=−0.1 (mm/min) for the loadthreshold L5, and the fast return is set to a fast return speed V6=−0.3(mm/min) for the load threshold L6. The emergency return is set to areturn speed V7 (full speed) for the load threshold L7.

In addition, because a return is in reverse direction to a cut-in, forthe sake of description of the slow return speed V4 etc., the numericalvalue is affixed with a minus sign − to indicate heading in the reversedirection.

The respective load thresholds L1 to L7 are, as illustrated in FIG. 6 interms of the load thresholds L1 to L4, in a relationship of a sequentialincrease from the load threshold L1 to the load threshold L7. The cut-inspeeds V0 to V3 and the return speeds V4 to V7 of the grinding wheel 1corresponding to the respective load thresholds L1 to L7 of the grindingload are predetermined by experimentation or the like so that thegrinding wheel 1 can efficiently grind the workpiece W in a moderatehigh-load state with high grinding efficiency in consideration of thecombination of the material and size of the workpiece W, the grindingwheel 1, the surface grinder 2, etc.

Accordingly, the high-speed cut-in, fast cut-in, intermediate cut-in,and slow cut-in decrease in speed in the cutting-in direction in stagesto the cut-in speeds V1 to V3 as the grinding load increases in stagesto the load thresholds L1 to L3. On the other hand, the slow return,intermediate return, fast return, and emergency return increase in speedin the returning direction in stages to the return speeds V4 to V7 asthe grinding load increases in stages to the load thresholds L4 to L7.The return speeds V4 to V7 of the grinding wheel 1, at which thegrinding wheel 1 moves in the direction reverse to the cutting-indirection, can therefore be said to decrease in stages from the slowreturn to the emergency return if the grinding wheel 1 is on the basisof the cutting-in direction.

In addition, when there is a standard speed table corresponding to astandard workpiece W, it also suffices to read out a numerical valuefrom the standard speed table according to the difference in thematerial etc., of the workpiece W and correct the same while performingcontrol.

As for the load threshold L3 for slow cut-in time and the load thresholdL4 for slow return time, the load threshold L4 for slow return time ishigher, and when a slow cut-in and a slow return are repeated multipletimes before spark-out after exceeding the load threshold L3, thegrinding wheel 1 is switched between the slow cut-in and slow return onthe basis of the load threshold L4 in such a manner as to, for example,perform a slow cut-in of the grinding wheel 1 when the grinding load isequal to the load threshold L3 or more and less than the load thresholdL4 and perform a slow return of the grinding wheel 1 when the grindingload is equal to the load threshold L4 or more.

Next, a grinding method for a workpiece W will be described withreference to the flowchart in FIG. 5. In-feed grinding of the workpieceW by the surface grinder 2 is performed through control of the NC means9. When the surface grinder 2 starts a grinding operation of in-feedgrinding (S1), the grinding wheel feed means 7 first feeds the grindingwheel spindle 5 in the cutting-in direction at a high-speed feed speedfaster than the high-speed cut-in speed V0 until immediately before thegrinding wheel 1 contacts the workpiece W. On the other hand, dimensionsof the workpiece W are measured by the size measuring means 12 (S2), agrinding load is measured by the grinding load measuring means 13 (S3),and the sizing control means 10 judges whether or not it is in aspark-out period (S4).

Immediately after the grinding operation is started, because it is notyet in a spark-out period (S4), it is determined whether or not thegrinding load is less than the load threshold L1 for a fast cut-in (S5),the feed speed of the grinding wheel spindle 5 is reduced from thehigh-speed feed speed to the high-speed cut-in speed V0, and thegrinding wheel 1 begins to grind the workpiece W at that high-speedcut-in speed V0 (S6).

Feeding the grinding wheel spindle 5 at a high-speed feed speed fasterthan the high-speed cut-in speed V0 until the grinding wheel 1 contactsthe workpiece W and reducing the feed speed to the high-speed cut-inspeed V0 immediately before the grinding wheel 1 contacts the workpieceW allows reducing air cut time to efficiently shift to grinding of theworkpiece W.

When the grinding wheel 1 contacts the workpiece W and starts grinding,a grinding load on the grinding wheel spindle 5 rises, but the grindingwheel 1 is caused to cut in forward at the high-speed cut-in speed V0 aslong as the grinding load is less than the load threshold L1 (S6). Then,when the grinding load rises due to the high-speed cut-in at thehigh-speed cut-in speed V0 to become equal to the load threshold L1 ormore and less than the load threshold L2 (S5, S7), the cut-in speed ofthe grinding wheel 1 is reduced from the high-speed cut-in speed V0 tothe fast cut-in speed V1 (S8), and the grinding wheel 1 is caused to cutin forward at that fast cut-in speed V1 while continuing the grinding ofthe workpiece W.

When the grinding load rises due to the fast cut-in at the fast cut-inspeed V1 to become equal to the load threshold L2 or more and less thanthe load threshold L3 (S7, S9), the cut-in speed of the grinding wheel 1is reduced from the fast cut-in speed V1 to the intermediate cut-inspeed V2 for intermediate cut-in (S10), and the grinding wheel 1 iscaused to cut in at that intermediate cut-in speed V2.

Also, when the grinding load rises due to the intermediate cut-in at thecut-in speed V2 to become equal to the load threshold L3 or more andless than the load threshold L4 (S9, S11), the cut-in speed of thegrinding wheel 1 is reduced from the intermediate cut-in speed V2 to theslow cut-in speed V3 for slow cut-in (S12), and the grinding wheel 1 iscaused to cut in at that slow cut-in speed V3 while continuing thegrinding of the workpiece W.

As above, grinding is started at the fast high-speed cut-in speed V0,and while the grinding load then rises from the load threshold L1through the load threshold L2 up to the load threshold L3 or more, thegrinding wheel 1 is decelerated in stages to the cut-in speeds V1 to V3while being caused to cut in forward.

In addition, if the grinding load falls in a manner such as to increasethe cut-in speed of the grinding wheel 1 from the slow cut-in speed V3to the intermediate cut-in speed V2 (S10) when the grinding load becomesless than the load threshold L3 during a slow cut-in of the grindingwheel 1 (S9), the cut-in speed of the grinding wheel 1 is increased withthe fall in grinding load.

When the grinding load rises during grinding at the slow cut-in speed V3to become equal to the load threshold L4 or more and less than the loadthreshold L5 (S11, S13), the grinding wheel 1 is returned by a slowreturn at the slow return speed V4 switched from the slow cut-in at theslow cut-in speed V3 while continuing the grinding of the workpiece W(S14). Also, when the grinding load becomes less than the load thresholdL4 during grinding by the slow return (S1), the grinding wheel 1 iscaused to cut in slowly by a slow cut-in at the slow cut-in speed V3switched from the slow return at the slow return speed V4 (S12).

Accordingly, when the grinding of the workpiece W proceeds until thegrinding load of the grinding wheel 1 reaches a high load region nearthe load threshold L4, the grinding wheel 1 thereafter performs a slowcut-in and a slow return one time or multiple times by repetition atloads higher or lower than the load threshold L3, L4 while continuinglater-stage grinding of the workpiece W.

The sizing control means 10 is also reading in the dimensions of theworkpiece W in the meantime, and when it reaches a spark-out periodwhere the dimensions are close to those of a predetermined finishingaccuracy (S4), the grinding wheel feed means 7 stops moving the grindingwheel 1 based on a spark-out instruction from the sizing control means10, and spark-out is performed in which the grinding wheel 1 grinds theworkpiece W at the stop position (S21). Then, the grinding is terminatedwhen the workpiece W has reached the finish dimensions due to thespark-out (S22).

In addition, when the grinding load becomes equal to the load thresholdL5 or more and less than the load threshold L6 during grinding by theslow return (S13, S15), the grinding wheel 1 is returned at theintermediate return speed V5 while continuing the grinding (S16), andfurther when the grinding load becomes equal to the load threshold L6 ormore and less than the load threshold L7 during that intermediate return(S15, S17), the grinding wheel 1 is returned at the fast return speed V6while continuing the grinding (S18).

Moreover, when the grinding load becomes equal to the load threshold L7or more (S17), an emergency return is performed at the emergency returnspeed V7 (full speed) (S19), and the grinding is suspended (S20). Then,after suspending the grinding, appropriate measures are implemented suchas performing dressing or the like of the grinding wheel 1 to regain thesharpness of the grinding wheel 1.

As above, a high-speed cut-in of the grinding wheel 1 is started at thehigh-speed cut-in speed V0, followed by monitoring variation in thegrinding load of the grinding wheel 1, while reducing the cut-in speedof the grinding wheel 1, with a sequential rise in the grinding loadfrom the load threshold L1 through the load threshold L2 to the loadthreshold L3, sequentially from that of a high-speed cut-in to that of afast cut-in, and from that of a fast cut-in to that of an intermediatecut-in, and from that of an intermediate cut-in to that of a slow cutin.

Accordingly, employing such a grinding method enables grinding theworkpiece W by the grinding wheel 1 so that the cut-in speed of thegrinding wheel 1 is almost coincident with a speed at which theworkpiece W is gradually ground by the grinding wheel 1, which allowsefficiently grinding the workpiece W with a moderate high load of highgrinding efficiency applied to the grinding wheel 1.

Particularly when the grinding wheel 1 is caused to cut in forward athigh speed, the speed at which the workpiece W is gradually ground bythe grinding wheel 1 and the cut-in speed of the grinding wheel 1 becomeno longer coincident with each other as the grinding proceeds, whichcauses grinding burrs on the workpiece W side to result in an abnormalrise in the grinding load of the grinding wheel 1. As a result,continuing the grinding remaining in the high-speed cutting-in stateresults in an excessively large load to be applied to the workpiece W tocause a problem such as splitting of the workpiece W. However, thegrinding load is monitored, while the cut-in speed of the grinding wheel1 is reduced with an increase in grinding load, and therefore, such acase as to the application of an excessively large load on the workpieceW can be prevented.

Also, in the later stage of the grinding of the workpiece W, because thegrinding wheel 1 is switched to a slow return if the grinding load risesto L4 during grinding by a slow cut-in after the grinding load rises tothe load threshold L3 or more, the workpiece W is ground in a high-loadstate with the slow cut-in and the slow return being repeated.Therefore, there is no such case that the grinding load of the grindingwheel 1 continues rising to apply an excessively large load on theworkpiece W, and the grinding can be continued at a moderate high loadof high grinding efficiency.

FIG. 6 shows changes in the grinding load and dimensions of workpieces Wwhen the workpieces W were actually ground. A is a grinding load curveshowing changes in grinding load from the start of grinding to the endof spark-out in the case of the present invention, and B is adimensional curve showing changes in the dimensions of the workpiece Win that case. A1 is a grinding load curve in the case of conventionalcommon grinding, and B1 is a dimensional curve showing changes in thedimensions of the workpiece W in that case.

With conventional common grinding, because the grinding is performedwith the cut-in speed of the grinding wheel 1 controlled depending onthe cutting-in feed amount of the grinding wheel 1 for a rough grindingfeed, a semi-finish grinding feed, and a finish grinding feed so as toprevent overloading, grinding at a slow cutting-in speed as shown by thegrinding load curve A1 in FIG. 6 is inevitable, so the grinding load ofthe grinding wheel 1 rises with the progress of grinding, but its pitchis gentle. Accordingly, because the workpiece W has been ground in alow-load state where loading of the grinding wheel 1 is likely to occurto hinder sufficiently displaying grinding efficiency, there hasconventionally been a problem such that the workpiece W has a prolongedgrinding cycle to lead to a rise in grinding temperature, in addition togrinding inefficiency.

On the other hand, with the present invention, as shown by the grindingload curve A in FIG. 6, the grinding wheel 1 is sequentially deceleratedwhile causing cut-in in an order of a high-speed cut-in, a fast cut-in,an intermediate cut-in, and a slow cut-in on the basis of the grindingload of the grinding wheel 1 every time the grinding load reaches apredetermined load threshold, and a slow cut-in and a slow return arerepeated a few times to shift to spark-out.

Because the self-sharpening effect of abrasive grains can therefore bepromoted by a rise in the grinding load of the grinding wheel 1, it ispossible to grind the workpiece W in a short time with high grindingefficiency, and grinding can be efficiently performed in a grindingcycle shorter than that of conventional common grinding. As a result,the grinding time with the present invention can be reduced to on theorder of approximately ⅔ compared with that in the case of conventionalcommon grinding, which proves that efficient grinding is possible. Also,with the present invention, because grinding is efficiently performed ata high load of high grinding efficiency, a rise in grinding temperaturecan be prevented as compared with the case of common grinding in whichgrinding is performed at a low grinding load.

FIG. 7 to FIG. 10 illustrate the second embodiment of the presentinvention. The grinding wheel cut-in/return control means 11 of thepresent embodiment has a speed limit implementing function, and as shownin FIG. 7, includes a speed limit implementation means 14A, besides agrinding load measuring means 13, a speed setting means 14, and a speedcontrol means 15 that are the same as with the first embodiment.

The speed limit implementation means 14A has a function of implementinga speed limit, when the grinding load of the grinding wheel 1 exceeds aload threshold LA for speed limit implementation, to limit the cut-inspeed of the grinding wheel 1 to a limit cut-in speed Vα (=0.03 mm/min)slower than the slow cut-in speed V3 (=0.05 mm/min) even if the grindingload thereafter falls to less than the load threshold L3 for a slowcut-in.

The speed table is configured as shown in FIG. 9, so as to deceleratethe grinding wheel 1 in stages to the cut-in speeds of V1 to V3 as thegrinding load increases in stages to the load thresholds L1 to 13,return the grinding wheel 1 at the slow return speed V4 (=−0.05 mm/min)when the grinding load rises to the load threshold L4 for slow returntime, limit the cut-in speed to the limit cut-in speed Vα (=0.03 mm/min)when the grinding load rises to the load threshold LA for the time ofspeed limit implementation, and suspend grinding when the grinding loadrises to a load threshold LX for the time of grinding suspension.

In in-feed grinding of the workpiece W, as shown in FIG. 8, it isdetermined whether or not the grinding load is equal to the loadthreshold LX for the time of grinding suspension or more (S23), and thegrinding is suspended (S24) if it is equal to the load threshold LX ormore. On the other hand, when the grinding load is less than the loadthreshold LX, it is checked whether or not the grinding load has reachedso far the load threshold LA for the time of speed limit implementationor more (S25), and if so even once, even when the grinding load is lessthan the load threshold L4 (S26), the grinding wheel 1 is limited to thelimit cut-in speed Vα (=0.03 mm/min) (S27). If the grinding load hasnever reached the load threshold LA or more, the grinding load iscompared with the load threshold L1 (S28), if less than the loadthreshold L1, the cut-in speed V0 for a high-speed cut-in is employed(S29). On the other hand, when the grinding load is equal to the loadthreshold L1 or more, if less than the load threshold L2 compared withthe load threshold L2 (S30), the cut-in speed V1 for a fast cut-in isemployed (S31).

Likewise, when the grinding load is equal to the load threshold L2 ormore, if less than the load threshold L3 compared with the loadthreshold L3 (S32), the cut-in speed V2 for an intermediate cut-in isemployed (S33). On the other hand, when the grinding load is equal tothe load threshold L3 or more, if less than the load threshold L4compared with the load threshold L4 (S34), the slow cut-in speed V3 fora slow cut-in is employed (S35). When the grinding load during grindingby a slow cut-in has reached the load threshold L4 or more, the grindingwheel 1 is returned at the slow return speed V4 (S36), in order toachieve a fall in grinding load by the slow return of the grinding wheel1.

Also during the grinding by a slow return, the grinding load of thegrinding wheel 1 is being compared with the load threshold LA for thetime of speed limit implementation (S37), and the process returns tostep S2 if it is less than the load threshold LA. However, if thegrinding load does not fall during grinding by a slow return and thegrinding load temporarily rises for some cause to the load threshold LAfor the time of speed limit implementation or more (S37), it ismemorized that the grinding load has exceeded the load threshold LA(S38), and the speed limit implementing function of the speed limitimplementation means 14A then works.

If the cause for the temporal rise in grinding load is thereaftereliminated, the grinding load suddenly falls due to the slow return atthe slow return speed V4 of the grinding wheel 1. However, because thegrinding load has once exceeded the load threshold LX (S25), even if thegrinding load of the grinding wheel 1 becomes less than the loadthreshold L4 for slow cut-in time (S26), the speed limit implementingfunction of the speed limit implementation means 14A works to limit asubsequent cut-in of the grinding wheel 1 to the slowest, limit cut-inspeed Vα (=0.03 mm/min) (S27) without employing the original slow cut-inspeed V3 (=0.05 mm/min).

Accordingly, there is no such case that the grinding wheel 1 and theworkpiece W repeat contact and separation. This is because, without thespeed limit implementing function, when the grinding load falls to lessthan the load threshold L3 during grinding of the workpiece W by a slowreturn (S34), the grinding wheel 1 is caused to cut in at the slowcut-in speed V3 by a slow cut-in switched from the slow return.Therefore, if the cut-in speed of the grinding wheel 1 is controlledaccording to a rise and fall in grinding load, the grinding wheel 1intensively move back and forth at a fast cutting-in speed and a fastreturning speed to cause repeated contact and separation between thegrinding wheel 1 and the workpiece W, so that the grinding of theworkpiece W may no longer proceed.

However, even when the grinding load falls to less than the loadthreshold L3 due to the slow return of the grinding wheel 1, thegrinding wheel 1 is caused to cut in slowly at a slower speed of thelimit cut-in speed Vα (=0.03 mm/min) without immediately causing cut-inat a faster speed of the cut-in speed V3 (=0.05 mm/min), so that asudden rise in the grinding load of the grinding wheel 1 can beprevented by switching from the slow return to the slow cut-in, andthere is no such case that the grinding wheel 1 intensively repeats areturn and a cut-in. Therefore, like the grinding load curve shown inFIG. 10, later changes in grinding load are stabilized, and theworkpiece W can be efficiently ground.

In addition, in the present embodiment, control is performed so as notto cause the grinding wheel 1 cut in at a speed faster than the limitcut-in speed Vα even when the grinding load falls after exceeding theload threshold LA for the time of speed limit implementation, but in thecase of returning the grinding wheel 1 as well, a limit return speed V1may be set so as not to cause a return at a return speed faster than thelimit return speed Vβ, after the grinding load exceeds a certain loadthreshold LB, even if there is such a case that the grinding loadthereafter falls to nearly above the load threshold L4.

FIG. 11 to FIG. 13 illustrate the third embodiment of the presentinvention. The grinding wheel cut-in/return control means 11 of thepresent embodiment, as shown in FIG. 11, has a table selection means 16capable of appropriately selecting a speed table stored in the speedsetting means 14, and configured so that the speed control means 15controls the grinding wheel feed means 7 according to the table selectedby the table selection means 16.

Examples of the tables stored in the speed setting means 14 include afirst speed table T1 shown in FIG. 12 and a second speed table T2 shownin FIG. 13. The table selection means 16 is not only capable ofindividually selecting the first speed table T1 and the second speedtable T2, but also capable of selecting a joint table for which bothspeed tables T1 and T2 are joined in part.

The joint table is a single speed table for which a front-behindrelationship of the first speed table T1 and the second speed table T2is selected and a speed table changing load when changing from that oneof the speed table T1 or the speed table T2 to another of the secondtable T2 or the speed table T1 is set to a load threshold appropriatelyand which is configured so as to join both speed tables T1 and T2 in amanner changed in the front-behind relationship at the speed tablechanging load, for switching from the one of the speed table T1 or thespeed table T2 to another of the second table T2 or the speed table T1at the speed table changing load.

For example, when selection is performed to have the first speed tableT1 in front and have the second speed table T2 behind and the loadthreshold L3 is set as the speed table changing load, a single speedtable for which a first half of the first speed table T1 up to the loadthreshold L3 and a second half of the second speed table T2 from theload threshold L3 onward are joined can be configured.

Accordingly, in in-feed grinding, the grinding wheel cut-in/returncontrol means 11 monitors a change in grinding load while respectivelycontrolling the cut-in speeds of the grinding wheel 1 according to thejoint table by its speed control means 15. For example, control isperformed according to the first speed table T1 in a first half of thegrinding, and a slow cut-in of the grinding wheel 1 is performed at aslow cut-in speed V3 (=0.05 mm/min) of the first speed table T1 when thegrinding load is less than the load threshold L3. Then, when thegrinding load becomes equal to the load threshold L3 or more, through achange from the first speed table T1 to the second speed table T2, aslow return of the grinding wheel 1 is performed at a slow return speedV3 (=−0.05 mm/min) according to the second speed table T2. In addition,other aspects of the configuration, control, etc., are the same as thoseof each embodiment.

Doing this allows configuration of a joint table by selectivelycombining the first speed table T1 with the second speed table T2 inpart, and grinding is possible under conditions optimal for the materialof the workpiece W and others despite the basis of the small number ofspeed tables T1 and T2.

In addition, there may be three types or more of speed tables, and maybe a plurality of types of speed table changing loads. Also, besideschanging tables depending on the speed table changing load, a pluralityof speed tables may be changed over on the basis of a cut-in time, acut-in amount, a removal amount read from a sizing device or the like.

FIG. 14 illustrates the fourth embodiment of the present invention. Inthe case of in-feed grinding a workpiece W by the grinding wheel 1, thegrinding load during grinding may rise or fall according to conditionsat that time. Accordingly, like the speed table shown in FIG. 14,whether or not to use a load threshold in which of a rising aspect and afalling aspect of the grinding load may be provided selectable (ON meansbeing selected, OFF means not being selected) in a speed table so as toappropriately select a necessary condition according to the grindingconditions.

In the case of the speed table in FIG. 14, there are control elements ofa high-speed cut-in, a fast cut-in, an intermediate cut-in, a slowcut-in, a slow return, an intermediate return, a fast return, and anemergency return, and the respective control elements can beappropriately selected according to the rising aspect or the fallingaspect. For example, in the rising aspect of the grinding load, theintermediate cut-in, slow return, and intermediate return are notselected, and the slow cut-in is not selected in the falling aspect.

In actual in-feed grinding, which of the rising or falling aspectsgrinding at that point in time is in may be judged by having determineda determination time on the order of a past few seconds-period andobtaining a moving average or the like of the grinding load in thatdetermination time.

FIG. 15 and FIG. 16 illustrate the fifth embodiment of the presentinvention. As shown in FIG. 15, the present grinding wheel cut-in/returncontrol means 11 has a grinding load measuring means 13 that measures agrinding load of the grinding wheel 1 during grinding, a speed settingmeans 14 that sets a cut-in speed or return speed of the grinding wheel1 for each load threshold, a time setting means 17 that sets anacceleration/deceleration time at the time of change in cut-in speed orat the time of switching between cut-in and return, and a speed controlmeans 15 that controls a cut-in or return of the grinding wheel feedmeans 7, through a comparison of a grinding load during grinding with aload threshold, to a cut-in speed or return speed set by the speedsetting means 14 according to an increase or decrease in the grindingload, and gently changes the speed unidirectionally in thatacceleration/deceleration time T set by the time setting means 17 at thetime of change in cut-in speed or at the time of switching betweencut-in and return.

In the grinding wheel cut-in/return control means 11 thus configured, ifthe acceleration/deceleration time T is preset by the time setting means17, a sudden change in speed can be prevented in either case of the timeof change in cut-in speed and the time of switching between cut-in andreturn, so that there is no such a problem that the grinding loadtemporarily falls, which allows efficiently grinding the workpiece W ata high grinding load.

For example, in the case of a decrease in speed from a high-speed cut-inat cut-in speed V0 to a fast cut-in at cut-in speed V1, because thespeed is gradually reduced from the cut-in speed V0 to the cut-in speedV1 in the acceleration/deceleration time T as shown by the solid line inFIG. 16(I), as compared with when immediately switching as shown by thedotted line, a sudden speed change can be suppressed to suppress achange in grinding load.

Also in the case of switching from a slow cut-in at cut-in speed V3 to aslow return at return speed V4 as well, because of gradual switchingfrom the cut-in speed V3 to the return speed V4 in theacceleration/deceleration time T as shown by the solid line in FIG.16(II), as compared with when immediately switching as shown by thedotted line, a sudden speed change in the reverse direction can besuppressed to suppress a change in grinding load.

In addition, the acceleration/deceleration time T can also beappropriately set according to the material etc., of the workpiece W.Also, the speed control means 15 may increase or reduce the speedgradually or in stages in accordance with predeterminedacceleration/deceleration characteristics at the time of change incut-in speed or at the time of switching between cut-in and return,besides enabling setting the acceleration/deceleration time T variable.

Although embodiments of the present invention have been described indetail hereinabove, the present invention should not be limited theretoand various modifications can be made. For example, load thresholds ofthe grinding load are desirably large in number. Accordingly, it is alsopossible to increase the number of load thresholds to a countlessnumber, and increasing the number of load thresholds to a countlessnumber enables a stepless speed change as well which reduces the cut-inspeed of the grinding wheel 1 with an increase in grinding load in astepless manner.

Also, in the embodiments, the workpiece W of a hard brittle material isexemplified, however, the present invention can likewise be carried outfor the whole of surface grinding of workpieces W of various materials,without limitation to hard brittle materials.

Although rotational load torque of the grinding wheel spindle 5 isexemplified as the grinding load, the grinding load may be judged basedon a change in the current or power of the grinding wheel drive means 6or a change in the load applied to the grinding wheel drive means 6, orthe grinding load may be judged based on a change in the torque,current, power, or load of the workpiece drive means 4. Also, in thecase of the surface grinder 2 without a workpiece drive mechanism, thegrinding load may be judged from a load on the workpiece W. Further, ajudgment may also be made in combination of two or more related factorsrelated to a change in grinding load, such as combination of a change inthe current, power, or load of the grinding wheel drive means 6 and achange in the current, power, or load of the workpiece drive means 4.

In the first and second embodiments, a detailed description has beengiven of the case of a rise in grinding load during cut-in, however,control may of course be performed so as to increase the cut-in speed ifthe grinding load falls under a predetermined load threshold duringcut-in. Also in that case, the cut-in speed may be increased over apredetermined time.

When the grinding load increases or reduces the cut-in speed on thebasis of a predetermined load threshold or performs switching betweencut-in and return, it suffices as long as a cut-in, return, or the likeof the grinding wheel 1 is possible on the basis of the predeterminedload threshold, and judging is also possible by either criterion ofbeing less than the load threshold or equal to the load threshold ormore.

The high-speed cut-in, fast cut-in, intermediate cut-in, slow cut-in,slow return, intermediate return, fast return, etc., are merelyexemplified, and the cut-in and return may be further finely divided, ormay be roughly divided into a smaller number. The values of therespective load thresholds, cut-in speeds, and return speeds are alsomerely exemplified, and are not limited thereto.

DESCRIPTION OF REFERENCE NUMERALS

-   1 Grinding wheel-   2 Surface grinder-   3 Rotating table-   4 Workpiece drive means-   5 Grinding wheel spindle-   7 Grinding wheel feed means-   10 Sizing control means-   11 Grinding wheel cut-in/return control means-   12 Size measuring means-   13 Grinding load measuring means-   14 Speed setting means-   14A Speed limit implementation means-   15 Speed control means-   16 Table selection means-   17 Time setting means

What is claimed is:
 1. A surface grinding method for a workpiececharacterized by, when surface-grinding a workpiece by a grinding wheel,monitoring a grinding load while reducing the grinding wheel in cut-inspeed with a rise in the grinding load.
 2. A surface grinding method fora workpiece characterized by, when surface-grinding a workpiece by agrinding wheel, monitoring a grinding load while reducing the grindingwheel in cut-in speed when the grinding load rises and increasing thecut-in speed when the grinding load falls.
 3. The surface grindingmethod for a workpiece according to claim 1, characterized by having setrespective cut-in speeds with which the grinding wheel has a slowercut-in speed at a larger grinding load, in a manner corresponding to aplurality of respective load thresholds of the grinding load, and afterstarting grinding at a predetermined speed, decelerating or acceleratingthe grinding wheel to a corresponding cut-in speed every time thegrinding load rises or falls to a predetermined load threshold.
 4. Thesurface grinding method for a workpiece according to claim 1,characterized by having set a returning load threshold higher than amaximum load threshold at cut-in time of the grinding wheel, andreturning the grinding wheel at a predetermined return speed whilegrinding when the grinding load exceeds the returning load threshold. 5.The surface grinding method for a workpiece according to claim 1,characterized by repeating a cut-in and return of the grinding wheelbefore spark-out.
 6. The surface grinding method for a workpieceaccording to claim 1, characterized by, when the grinding load exceeds aload threshold for implementation of a speed limit, even if the grindingload thereafter falls to a load threshold of a predetermined cut-inspeed, causing the grinding wheel to cut in at a limit cut-in speedslower than the predetermined cut-in speed, or not making the cut-inspeed faster than the limit cut-in speed.
 7. The surface grinding methodfor a workpiece according to claim 3, characterized by having set areturning load threshold higher than a maximum load threshold at cut-intime of the grinding wheel, and returning the grinding wheel at apredetermined return speed while grinding when the grinding load exceedsthe returning load threshold.
 8. The surface grinding method for aworkpiece according to claim 3, characterized by repeating a cut-in andreturn of the grinding wheel before spark-out.
 9. The surface grindingmethod for a workpiece according to claim 3, characterized by, when thegrinding load exceeds a load threshold for implementation of a speedlimit, even if the grinding load thereafter falls to a load threshold ofa predetermined cut-in speed, causing the grinding wheel to cut in at alimit cut-in speed slower than the predetermined cut-in speed, or notmaking the cut-in speed faster than the limit cut-in speed.
 10. Thesurface grinding method for a workpiece according to claim 4,characterized by, when the grinding load exceeds a load threshold forimplementation of a speed limit, even if the grinding load thereafterfalls to a load threshold of a predetermined cut-in speed, causing thegrinding wheel to cut in at a limit cut-in speed slower than thepredetermined cut-in speed, or not making the cut-in speed faster thanthe limit cut-in speed.
 11. The surface grinding method for a workpieceaccording to claim 2, characterized by having set respective cut-inspeeds with which the grinding wheel has a slower cut-in speed at alarger grinding load, in a manner corresponding to a plurality ofrespective load thresholds of the grinding load, and after startinggrinding at a predetermined speed, decelerating or accelerating thegrinding wheel to a corresponding cut-in speed every time the grindingload rises or falls to a predetermined load threshold.
 12. The surfacegrinding method for a workpiece according to claim 2, characterized byhaving set a returning load threshold higher than a maximum loadthreshold at cut-in time of the grinding wheel, and returning thegrinding wheel at a predetermined return speed while grinding when thegrinding load exceeds the returning load threshold.
 13. The surfacegrinding method for a workpiece according to claim 2, characterized byrepeating a cut-in and return of the grinding wheel before spark-out.14. The surface grinding method for a workpiece according to claim 2,characterized by, when the grinding load exceeds a load threshold forimplementation of a speed limit, even if the grinding load thereafterfalls to a load threshold of a predetermined cut-in speed, causing thegrinding wheel to cut in at a limit cut-in speed slower than thepredetermined cut-in speed, or not making the cut-in speed faster thanthe limit cut-in speed.
 15. The surface grinding method for a workpieceaccording to claim 11, characterized by having set a returning loadthreshold higher than a maximum load threshold at cut-in time of thegrinding wheel, and returning the grinding wheel at a predeterminedreturn speed while grinding when the grinding load exceeds the returningload threshold.
 16. The surface grinding method for a workpieceaccording to claim 11, characterized by repeating a cut-in and return ofthe grinding wheel before spark-out.
 17. The surface grinding method fora workpiece according to claim 11, characterized by, when the grindingload exceeds a load threshold for implementation of a speed limit, evenif the grinding load thereafter falls to a load threshold of apredetermined cut-in speed, causing the grinding wheel to cut in at alimit cut-in speed slower than the predetermined cut-in speed, or notmaking the cut-in speed faster than the limit cut-in speed.
 18. Thesurface grinding method for a workpiece according to claim 12,characterized by repeating a cut-in and return of the grinding wheelbefore spark-out.
 19. The surface grinding method for a workpieceaccording to claim 13, characterized by, when the grinding load exceedsa load threshold for implementation of a speed limit, even if thegrinding load thereafter falls to a load threshold of a predeterminedcut-in speed, causing the grinding wheel to cut in at a limit cut-inspeed slower than the predetermined cut-in speed, or not making thecut-in speed faster than the limit cut-in speed.
 20. A surface grinderwhich in-feed grinds a workpiece by a grinding wheel, characterized bycomprising: a grinding load measuring means that measures a grindingload of the grinding wheel during grinding; a speed setting means inwhich a plurality of grinding wheel cut-in speeds are set correspondingto a plurality of load thresholds; and a speed control means thatcompares the grinding load during grinding with a load threshold whileaccelerating or decelerating the grinding wheel, on the basis of eachload threshold, at a cut-in speed corresponding to each load thresholdso that the grinding wheel is reduced or increased in cut-in speed witha rise or fall in the grinding load.